1. Field of the Invention
The present invention relates generally to the testing of medical electrodes that are mounted on a release liner. More particularly, the invention is directed to various electrode and/or release liner embodiments that facilitate testing and characterization of packaged electrodes.
2. Description of the Background Art
Sudden Cardiac Arrest (SCA) is one of the leading causes of death in the industrialized world. SCA typically results from an arrhythmia condition known as Ventricular Fibrillation (VF), during which a patient""s heart muscle exhibits extremely rapid, uncoordinated contractions that render the heart incapable of circulating blood. Statistically, after four minutes have elapsed, the patient""s chance of survival decreases by 10% during each subsequent minute they fail to receive treatment.
An effective treatment for VF is electrical defibrillation, in which a defibrillator delivers an electrical pulse, waveform, or shock to the patient""s heart. Because the onset of VF is generally an unpredictable event, the likelihood that a victim will survive increases dramatically if 1) defibrillation equipment is nearby; 2) such equipment is in proper working order; and 3) such equipment may be easily, rapidly, and effectively deployed to treat the patient.
Medical equipment manufacturers have developed Automated External Defibrillators (AEDs) that minimally trained personnel may use to perform electrical defibrillation when emergency situations arise. AEDs may be found in a variety of non-medical settings, including residences, public buildings, businesses, private vehicles, public transportation vehicles, and airplanes.
An AED relies upon a set of electrodes to deliver a series of shocks to a patient. An electrode therefore serves as a physical and electrical interface between the AED and the patient""s body. In general, an electrode may comprise a conductive foil layer that resides upon a conductive adhesive layer; a lead wire that couples the foil layer to the AED; and an insulating layer that covers the foil layer. The conductive adhesive layer physically and electrically interfaces the foil layer to a patient""s skin. New or unused electrodes reside upon a release liner, from which an operator may peel off an electrode prior to placement upon a patient""s body. During manufacture, electrodes upon their release liner are typically sealed in a package.
An AED is likely to be used infrequently; however, any given use may involve a time critical, life threatening situation. Thus, it is imperative that the AED be able to provide an indication of its operating condition at essentially any time. While in a quiescent state, an AED generally performs periodic diagnostic sequences to determine its current operating condition. Such sequences may be performed, for example, on a daily and/or weekly basis. The diagnostic sequences include tests for characterizing the current path between the AED and a set of electrodes. Hence, the electrodes must be connected to the AED while the AED is in its quiescent state, and the electrodes must be electrically testable while mounted on their release liner. As a result, release liners providing electrical contact between electrodes have been developed.
Such release liners generally include multiple openings that facilitate electrical contact between electrodes. The current path between the AED and the electrodes includes each electrode""s lead wire, foil layer, and conductive adhesive layer. For a pair of new, properly functioning conventional electrodes mounted upon a release liner having multiple openings, this current path may be characterized by an impedance value ranging between 2 and 10 Ohms. If an impedance measurement indicates an electrical discontinuity or open circuit condition exists, a lead wire or connector coupling an electrode to the AED may be damaged, and/or an electrode may be improperly connected to the AED. Similarly, if an impedance measurement indicates a short or open circuit condition exists, one or more electrodes, a lead wire or other wire within the current path, and/or a connector that couples the electrodes to the AED may be damaged or defective.
A measurement indicating a higher than desired impedance may arise when an electrode is damaged, deteriorated, and/or degraded. An electrode""s conductive adhesive layer typically comprises a hydrogel film, which itself comprises natural and/or synthetic polymers dispersed or distributed in an aqueous fluid. The electrical properties of the hydrogel film are dependent upon its moisture content. If the hydrogel possesses appropriate water content, it provides a low impedance electrical path between the electrode""s foil layer and a patient""s skin. The hydrogel film, however, dries out over time. As a result, its impedance increases over time, thereby undesirably decreasing its effectiveness for signal exchange and energy transfer between a patient and an AED. Once moisture loss has reached a certain level, the hydrogel film, and hence the electrode of which it forms a part, may be unsuitable for use.
A patient""s transthoracic impedance typically falls within a range of 25 to 200 Ohms. As electrodes"" hydrogel film deteriorate over time, the impedance associated with the electrical path provided by the electrodes may overlap with the typical transthoracic impedance range. Thus, if an AED in a normal operational or xe2x80x9conxe2x80x9d state measures an electrode impedance corresponding to a patient""s transthoracic impedance, the AED has no inherent way of determining whether partially deteriorated electrodes are currently mounted upon their release liner, or properly functioning electrodes are connected to the patient.
Prior release liners that facilitate electrical testing of electrodes mounted thereupon have typically been unnecessarily complex, expensive to manufacture, unacceptable relative to difficulty of electrode removal, and/or limited relative to the extent to which they permit accurate characterization of an electrode""s hydrogel film. A need exists for electrodes and/or release liners that overcome the aforementioned deficiencies.
The present invention includes a number of release liner, electrode, and/or medical or measuring device embodiments that facilitate electrical characterization of one or more electrodes coupled to the medical or measuring device. In the context of the present invention, a medical device may be essentially any device capable of using electrodes to receive signals from and/or deliver signals and/or energy to a patient""s body. A measuring device may be essentially any device capable of electrically characterizing packaged electrodes.
In one embodiment, a release liner comprises a release layer and a moisture-permeable and/or moisture-absorbent membrane or sheet. The release layer may include an opening therein, over which the membrane may reside. When electrodes are positioned or mounted upon the release liner, the electrodes"" conductive adhesive or hydrogel layers may transfer moisture to the membrane, thereby forming a low impedance electrical path that facilitates electrical communication between electrodes. The membrane may be prewetted or premoistened prior to mounting electrodes upon the release layer to minimize electrode moisture loss.
The release layer may comprise a single, foldable sheet that surrounds or partially surrounds the membrane. A pair of electrodes residing upon the same side of the foldable sheet may exchange electrical signals. Alternatively, a first and a second release layer may encase or enclose one or more portions of the membrane, where each release layer includes an opening. In another release liner embodiment, a membrane may extend beyond a border of a single release layer that lacks openings. Electrodes mounted upon the release layer in such an embodiment also extend beyond the release layer border, and contact the membrane to facilitate electrical communication therebetween.
A release liner and electrode package according to an embodiment of the invention may comprise a rigid cartridge having an electrical interface incorporated therein; a release liner having a set of openings therein; and a set of electrodes mounted upon the release liner. The openings in the release liner facilitate electrical communication between electrodes. The rigid cartridge provides an environment characterized by well-defined internal conditions, where moisture transfer in or out of the rigid cartridge is minimal or essentially eliminated. Such a package may therefore prolong electrode lifetime.
A release liner according to another embodiment of the invention may comprise a release layer upon which a conductive strip resides. Electrodes may be mounted in a side-by-side manner upon the release layer, and may exchange electrical signals via the conductive strip. The release layer may comprise a foldable sheet. In an alternate embodiment, the conductive strip may wrap around or encircle the release layer, facilitating electrical communication between electrodes mounted on opposite sides of the release layer.
A release liner according to another embodiment of the invention may comprise a release layer having a set of openings therein, and a conductive backing layer. The release layer may comprise a foldable sheet. Electrodes may be mounted upon such a release liner in a side by side manner. An electrical signal may travel from one electrode, through an opening in the release layer, through or within the conductive backing layer, through another opening in the release layer, and into another electrode.
The conductive backing layer may comprise a metal, or a conductive adhesive layer such as a hydrogel layer. In the event that the conductive backing layer comprises a conductive adhesive layer, an electrical current traveling between mounted electrodes may follow a path that is much greater than the thickness of the electrodes"" conductive adhesive layers. As a result, the measured impedance of the release liner may be greater than typical patient impedance ranges, and may exhibit a high degree of sensitivity to conductive adhesive layer degradation over time.
A release liner according to another embodiment of the invention may comprise a first release layer or sheet, a second release layer or sheet, and an intervening conductive adhesive layer. The first and second release layers each include an opening. The first and second release layers are oriented or positioned such that their openings are offset relative to each other by a separation distance. Electrodes mounted upon the release layers may exchange electrical signals with each other via the release layer openings and the conductive adhesive layer between the release layers. Such electrical signals may travel through a length of conductive adhesive layer that is much greater than the thickness of the electrodes"" conductive adhesive layers, in a manner analogous to that described above. In an alternate embodiment, a release liner may comprise a foldable sheet that surrounds or encases one or more portions of a conductive adhesive or hydrogel layer. The foldable sheet may include openings, which are offset relative to each other in accordance with a given separation distance when the foldable sheet surrounds or encases portions of the conductive adhesive layer.
An electrode according to an embodiment of the invention may comprise a conductive adhesive layer coupled to a conductive foil layer that includes one or more voids therein. Each void affects electrical current flow through the electrode""s conductive adhesive layer when the electrode is mounted upon a release liner that facilitates electrical communication between electrodes. In particular, the presence of a void may cause transverse electrical current flow through the electrode""s conductive adhesive layer, rather than simply current flow through the conductive adhesive layer""s thickness. This results in a longer electrical path, which in turn may provide the voided electrode with an impedance that is greater than typical patient impedance levels. Additionally, impedance measurements along this electrical path may exhibit a significant degree of sensitivity to changes in conductive adhesive layer properties over time.
An electrode may include or incorporate one or more insulating swatches between its conductive foil layer and conductive adhesive layers. When the electrode is mounted upon a release liner that facilitates electrical communication between electrodes, the presence of an insulating swatch may result in transverse current flow through the electrode""s conductive adhesive layer in a manner analogous to that described above for the voided electrode.
An electrode according to another embodiment of the invention may comprise a conductive foil layer, a conductive adhesive layer, and a sonomicrometer or ultrasonic transducer. When electrodes that incorporate ultrasonic transducers are mounted upon a release liner, ultrasonic signals transmitted and/or received via the ultrasonic transducers may be used to indicate an electrode separation distance. The electrode separation distance may indicate whether electrodes are mounted upon a release liner or a patient""s body.
In accordance with the present invention, various types of electrodes may be mounted upon release liners that facilitate exchange of electrical signals between electrodes. A medical device to which such electrodes are coupled may perform a variety of measurements to characterize electrode condition or fitness for use. The medical device may measure a short or open circuit condition, which may indicate an electrical path problem. As one or more electrodes"" conductive adhesive layers degrade over time, the medical device may measure increasing impedance levels. If an impedance level exceeds a given threshold value or range, the medical device may provide an indication that the electrodes are non-optimal or unfit for use. The medical device may alternately or additionally provide an indication of electrode condition or fitness for use at particular times or time intervals. The medical device may further calculate or determine a time remaining before an electrode or electrode pair may no longer be fit for use. Such a calculation or determination may be based upon a current degradation curve.
In accordance with an embodiment of the invention, a release liner that lacks openings may serve as a capacitive medium between electrodes mounted thereupon. A medical device may perform a capacitance measurement to electrically characterize an electrical path corresponding to the electrodes and release liner.
In accordance with another embodiment of the invention, a release liner may comprise a release layer that includes an opening, and an insulating swatch or patch that covers or resides within the opening. Electrodes may be mounted upon the release layer such that the electrodes"" conductive adhesive layers cover the opening, and at least one electrode""s conductive adhesive layer covers the swatch.
A medical device may perform a complex impedance measurement upon electrodes mounted upon a release liner having such a swatch. When one or more such electrodes include a void or internal swatch as described above, the result of the complex impedance measurement may exhibit significant dependence upon the current condition of such electrodes"" conductive adhesive layers. The medical device may therefore determine an extent to which one or more electrodes are fit for use. The medical device may further provide a visual and/or other indication of electrode condition and/or fitness for use.
A medical device such as an Automated External Defibrillator (AED) may include or incorporate elements for periodically determining electrode condition or status. The medical device may include a status measurement unit, which may operate in conjunction with an electrode condition indicator, a display device, a speaker, and/or other elements in a variety of manners to indicate electrode condition, fitness for use, and/or an estimated remaining electrode lifetime. In accordance with an embodiment of the invention, an electrode condition indicator may incorporate, generate, and/or present one or more types of visual metaphors that provide an indication of electrode status, condition, and/or estimated remaining lifetime. A visual metaphor may correspond to a fuel gauge, and may convey positional and/or color relationships between one or more indicating elements that change or vary over time in accordance with measured and/or estimated electrode properties. The visual metaphor may further convey textual and/or symbolic information.